Question

State the role of silica in the metallurgy of copper.

Answer 1

Metallurgy is a branch that is related with study of physical and chemical properties of metals. The study includes production, phase transformation, characterization and chemical reactivity.

Complete step by step answer: Silica is silicon dioxide which is acidic in nature. Due to acidic nature it shows the tendency to react with basic metal oxides.
Copper is an element in the periodic table with atomic number $29$ and electronic configuration$\left[ {Ar} \right]3{d^{10}}4{s^1}$. It is obtained from nature from various ores. The major ore is known as pyrite ore which contains a mixture of iron and copper sulfide with chemical formula$CuFe{S_2}$ . It is also known as chalcopyrite.
The ore of copper is extracted using a roasting and smelting process. The first step roasting involves the oxidation of chalcopyrite in presence of molecular oxygen. The corresponding reaction leads to formation of iron oxide, copper oxide and sulfur dioxide. The reaction is written as:
$2CuFe{S_2} + {O_2} \to 2FeS + C{u_2}S + S{O_2}$
$2FeS + 3{O_2} \to 2FeO + 2S{O_2}$
$2C{u_2}S + 3{O_2} \to 2C{u_2}O + 2S{O_2}$
The next step is the smelting of the generated products after roasting in large blast furnaces. The significance of smelting is to remove the unwanted iron and sulfur intermediates from the copper compound. For this purpose the silica gel is employed.
Silica is an oxide of silicon represented as $Si{O_2}$. It is acidic in nature and reacts with basic substances. The role of silica gel is to bind with the iron oxide from the mixture. The silica acts as a flux and readily combines with $FeO$ and produces iron silicate $FeSi{O_3}$ . The reaction is written as
$FeO + Si{O_2} \to FeSi{O_3}$
The slag thus formed is less dense than matte and floats over matte and is removed.

Note:
The use of silica also reduces the melting point of slag and thus the smelting process is achieved at low temperature. As a result the loss of copper is minimized.